Internal combustion engines, and particularly diesel engines, are difficult to start when the fuel, the engine cooling medium, and the engine are cold. When cold, diesel fuel can gel and solidify in the fuel filter and pump. Even when the engine is running, the high viscosity, lower grade No. 2 diesel fuel is prone to gel and cause the engine to stall by clogging fuel line filters and the fuel injection pump. Yet the No. 2 grade diesel fuel is lower in cost than the higher grade No. 1 fuel.
Preheating the fuel prior to combustion promotes greater efficiency of combustion. It also prevents gelling and solidifying of the fuel. Prior art devices have provided for means to preheat fuel through the use of the heated cooling medium of the engine prior to combustion. For example, see U.S. Pat. No. 1,300,600 to Giesler, and U.S. Pat. No. 3,354,872 to Gratzmuller. A common practice is to maintain a diesel engine running throughout periods of non-use to prevent the difficulty encountered when starting it again. Thus, it is also desirable to maintain the fuel heated when the engine is not running to facilitate starting of the engine and to allow the use of a more economical grade of fuel.